Traditionally, inhalation therapy has played a relatively minor role in the administration of biotherapeutics and conventional pharmaceuticals when compared to more traditional drug administration routes, such as oral and intraveneous. Injection is still the customary route of delivery of biotherapeutics (e.g., peptides, proteins and nucleic acids), and due to the many drawbacks associated with injection (e.g., inconvenience, discomfort, patient aversion to needle-based delivery methods), alternative administration routes are needed.
Pulmonary delivery is one such alternative administration route which can offer several advantages over needle-based administration. These advantages include the convenience of patient self-administration, the potential for reduced drug side-effects, ease of delivery by inhalation, the elimination of needles, and the like. Many preclinical and clinical studies with inhaled proteins, peptides, DNA and small molecules have demonstrated that efficacy can be achieved both within the lungs and systemically. However, despite such results, the role of inhalation therapy in the health care field has not grown as expected over recent years, in part due to a set of problems unique to the development of inhaleable drug formulations. In particular, dry powder formulations for pulmonary delivery, while offering unique advantages over cumbersome liquid dosage forms and propellant-driven formulations, can be prone to aggregation and low flowability phenomena which considerably diminish the efficiency of dry powder-based inhalation therapies.
In recent years, driven in part by the interest in aerosol delivery of dry powders and some of the short-comings of well-known techniques for preparing dry powders (e.g., lyophilization, air-drying, and co-precipitation), spray drying has been employed as a method for preparing micron-sized powders for pulmonary administration (Platz, R., et al., International Patent Publication No. WO 96/32149). Spray drying utilizes a hot gas stream to evaporate microdispersed droplets created by atomization of a liquid feedstock to form dry powders. While spray-drying has been long employed in the food and pharmaceutical industries to prepare dry powders, its application to therapeutic proteins has been rather limited because of the concern that certain proteins may be thermally degraded during the spray drying process. While there is now a growing body of evidence to support the general utility of spray drying macromolecule-based biotherapeutic formulations to produce biologically active powders suitable for inhalation (Foster, L., et al., International Patent Publication No. WO 98/16205; Platz, R., et al., International Patent Publication No. WO 97/41833; Eljamal, M., et al., International Patent Publication No. WO 96/32152, Eljamal, M., et al., International Patent Publication No. 96/32116; Eljamal, M., et al., International Patent Publication No. 95/24183; Bennett, D., et al., International Patent Publication No. 01/00312), many peptides and proteins, when exposed to the harsh conditions of spray drying, are prone to a certain degree of aggregation (unfolding).
Certain proteins, and in particular, proteins characterized as belonging to the 4-α-helical bundle superfamily (e.g., hGH, INF-γ, INF-β, GM-CSF, M-CSF, IL-2, IL-4, IL-5). are extremely susceptible to denaturation, unfolding, aggregation and precipitation, with loss of biological activity. These proteins share extensive sequence and structural (conformational) homology, characterized by a protein core folded in an up, up, down, down, antiparallel, left handed for α-helix bundle with a double-overhand loop topology. Thus, due to their instability, spray-drying and formulating this class of proteins for inhalation presents a unique set of challenges.
Several aspects of the spray-drying process can contribute to protein unfolding for this class of proteins, such as shear stress, high temperatures, exposure of a protein in a droplet to the liquid air interface (surface effects), liquid-wall interactions, and the like, and can result in the formation of dried particles which contain a high degree of protein in aggregated form that are in a size range unsuitable (or at least non-optimal) for inhalation. Examples of 4-α-helix bundle protein instability upon processing are numerous. Recombinant consensus α-interferon (rConIFN) was shown to be destabilized by air-jet nebulization, which resulted in rapid formulation of insoluble noncovalent aggregates, with only about 25% of the initial monomeric protein remaining after 25 minutes of nebulization. (Ip, A. Y., et al., J. Pharm Sci., 84(10), 1995: 1210-1214). In an examination of the feasibility of spray-drying proteins such as hGH, 25% of the protein was found to be degraded during processing, although addition of 0.1% (w/v) polysorbate 20 reduced the formation of insoluble and soluble aggregates during spray drying by about 70-85% (Mumenthaler, M., et al., Pharm. Research, 11 (1), 1994: 12). The addition of polysorbate 20 in the presence of divalent zinc ions was found to further suppress hGH degradation upon spray-drying (Maa, Y-F., et al., J. Pharm. Sci., 87 (2), 1998: 152-159). In an investigation of the bioactivity and physical stability of interleukin-2 upon delivery by continuous infusion, transient surface association of IL-2 with the catheter tubing was identified as being responsible for the majority of the biological activity loss observed (˜90% loss) (Tzannis, S., et al., Proc. Natl. Acad. Sci. USA, 93: 5460 (1996).
Of the 4α-helix bundle proteins, growth hormone is particularly unstable, and many approaches have been employed to date to arrive at stable therapeutic formulations. Degradation products of growth hormone include deaminated or sulfoxylated products and dimer or polymer forms. Specifically, the predominant degradation reactions of growth hormone are (i) deamidation by direct hydrolysis or via a cyclic succinimide intermediate to form various amounts of L-asp-hGH, L-iso-asp-hGH, D-asp-hGH, and D-iso-asp-hGH, and (ii) oxidation of the methionine residues in positions 14 and 125. Human growth hormone is also readily oxidized in positions 14 and 125. More importantly, aggregate formation in human growth hormone is detrimental, since this can lead to reduced bioactivity and increased immunogenicity (Becker, et al., Biotech. Appl. Biochem., 9:478-487 (1987); Leppert, P., Moore, W. V., J. Clin. Endocrinol., 51: 691-697 (1980)).
Thus, protein denaturation, the formation of aggregates, and production of powders having poor flow properties and low dispersibilities continue to plague development efforts to prepare aerosolizable 4-helix bundle protein powders for inhalation therapy. Moreover, many of the approaches utilized to date are undesirable or unsuited for powder formulations for inhalation therapies, such as the use of surfactants, which are thought to interfere with the lung pathology and are epithelial irritants, or increasing the protein solids concentration of pre-spray dried solutions, which can result in particles that are too big for efficient delivery to the deep lung.
Thus, a need exists for improved inhaleable powder aerosols for the pulmonary delivery of 4-helix bundle proteins, and in particular, for spray-dried powders having excellent aerosol properties and reduced aggregation.